Mullerian Inhibition Substance, a product of mammalian testes both during fetal development and immediately after birth, is responsible for the regression of the male Mullerian duct, a structure which, in the female, develops into uterus, fallopian tubes, and upper vagina. The major objectives of this proposed work are to isolate and purify Mullerian Inhibiting Substance, to elucidate at the ultrastructural level the mechanism by which the intracellular hormone initiates the death and disappearance of the Mullerian duct cells, to investigate the endocrine modulators of Mullerian Inhibiting Substance production and its role in the normal sexual differentiation, and to study the potential role of Mullerian Inhibiting Substance as an inhibitor of tumors of Mullerian duct origin. Extracts of whole testes demonstrate Mullerian Inhibiting Substance activity in an organ culture assay. Column chromatography and disc gel electrophoresis of the extracts indicate that Mullerian Inhibiting Substance is a protein of 100-150,000 molecular weight which elutes early on a diethylaminoethane column. Electron microscopy both in vivo and in vitro demonstrates that the Mullerian ducts undergo increased lysosome formation followed by autophagocytosis. Pituitary gonadatropins may inhibit Mullerian Inhibiting Substance production since an antibody to Leutinizing Hormone, Releasing Hormone, increases Mullerian Inhibiting Substance activity after birth. Extracts of Mullerian Inhibiting Substance are being studied for their cytotoxic potential against tumors of Mullerian duct origin. BIBLIOGRAPHIC REFERENCES: Donahoe, P.K., Ito, Y., Marfatia, S., Hendren, W.H., The production of Mullerian Inhibiting Substance by the fetal, neonatal and adult rat, Biol. Reprod. 15:329, 1976. Donahoe, P.K., Ito, Y., Price, J.M., Hendren, W.H., Mullerian Inhibiting Substance activity in bovine fetal, newborn, and prepubertal testes, Biol. of Reprod. 16:238, 1977.